The present disclosure relates to a transmission device, a transmission/reception device, and an integrated circuit, each of which has a function of performing non-contact communication (transmission) of information or energy by electromagnetic induction (electromagnetic coupling), and communication state monitoring methods of these devices.
Nowadays a non-contact communication system in which non-contact IC (Integrated Circuit) cards, such as a traffic ticket and electronic money, are used becomes significantly widespread. In such a non-contact communication system, a transmission signal (electromagnetic wave) emitted from a transmission antenna (a resonant circuit) of a reader/writer (hereinafter abbreviated to as R/W) device dedicated to the system is received by the electromagnetic induction using a reception antenna provided in the non-contact IC card.
In such a non-contact communication system, it is important to mutually match a frequency of a signal source of the R/W device, a resonance frequency of the transmission antenna of the R/W device, and a resonance frequency of the reception antenna (resonant circuit) of the non-contact IC card, so as to obtain good communication characteristic. However, the resonance frequency of the reception antenna of the non-contact IC card or the transmission antenna of the R/W device is varied by various factors. In this case, it is difficult to stably transmit and receive information between the non-contact IC card and the R/W device.
Thus, in the past, in the technical field of non-contact communication systems, there have been proposed various technologies for maintaining a good communication state under all conditions (see, for example, Patent Literature 1). Patent Literature 1 describes a non-contact IC card device for an electronic settlement system that performs electronic settlement by wireless communication. In the non-contact IC card device for the electronic settlement system of Patent Literature 1, there is proposed a technology for optimally controlling transmission power of a wireless transmission/reception circuit according to a distance or a position relationship between a wireless transmission/reception circuit and a non-contact R/W and a surrounding radio wave condition.